The published document DE 10 2013 008 757 A1 describes a wrist unit of an industrial robot, said wrist unit comprising a first wrist element, which is mounted rotatably about a first axial line at a first joint of a front end side of a robot arm; a second wrist element that is mounted rotatably about a second axial line at a second joint of a front end side of the first wrist element, wherein the second axial line is not located on an extension of the first axial line and is not parallel to the first axial line; a third wrist element that is mounted rotatably about a third axial line at a third joint of a front end side of the second wrist element, wherein the third axial line is not located on an extension of the second axial line and does not extend parallel to the second axial line; a driving motor for the second wrist, where said motor is provided on the first wrist element or the robot arm, in order to control the second wrist element; a driving motor for the third wrist, where said motor is provided on the first wrist element or the robot arm, in order to control the third wrist element; an eccentrically oscillating speed-changing transmission that is provided at the second joint in such a way that an axial center line of rotation fits together with the second axial line, in order to slow down a rotation of the driving motor for the second wrist and to transmit to the second wrist element, wherein the eccentrically oscillating speed-changing transmission comprises a hollow shaping member that forms a hollow body along the axial center line of rotation; and a through shaft that is mounted rotatably on the hollow shaping member and extends through the hollow body, in order to transmit a rotation from the driving motor for the third wrist from one side of the first wrist element to a side of the second wrist element; a plurality of crankshafts that are arranged around the through shaft, wherein the plurality of crankshafts comprises input gearwheels provided at the ends of the side of the first wrist element; and a transmission member that is provided centrally in a manner allowing rotation about the axial center line of rotation, wherein the transmission member comprises a first gearwheel, to which a rotational force is supplied by the driving motor for the second wrist element, and a second gearwheel, with which the input gearwheels of the plurality of crankshafts are in engagement.
The published document DE 10 2010 016 952 A1 discloses a harmonic drive reduction gear for a robot, with a housing, comprising a frame, formed in the housing; a circular spline fixed to the frame and having an edge region that is provided with internal gear teeth; a cylindrical flex spline that is inserted into the circular spline and that has an outer edge area, which is provided with external gear teeth meshing with the internal gear teeth, wherein the flex spline is connected to an output shaft; and an elliptical wave generator, which is fitted into the flex spline and which is connected to a drive shaft.
The object of the present invention is to provide a transmission and an electric driving device, in particular, an industrial robot with such a transmission or such an electric driving device, with the transmission and the electric driving device respectively being compact and, in particular, also light.